A lightning shielding failure risk assessment method for transmission lines based on three-dimensional laser point cloud

Abstract

A transmission line lightning shielding failure risk assessment method based on three-dimensional laser point cloud includes the following steps: reclassifying the three-dimensional laser point cloud data of the transmission channel; obtaining the lightning activity parameters of the transmission channel; calculating the strike distance of the conductor, ground wire and ground point; drawing the three-dimensional shielding arc surface of the conductor, ground wire and ground point in the preprocessed three-dimensional laser point coordinate system; orthogonally projecting the drawn three-dimensional shielding arc surface to obtain a two-dimensional exposed arc surface, and calculating the two-dimensional exposed arc surface area; looping steps 3-5, calculating the exposed arc surface area under different lightning current amplitudes and lightning incident angles, and calculating the line tripping rate by combining the lightning density, lightning incident angle distribution function and lightning current probability distribution function. Without the need for complex two-dimensional slicing, parameter extraction and shielding arc geometric relationship judgment, the rapid calculation of the three-dimensional exposed arc surface area of ​​the transmission line and the accurate assessment of the line shielding failure tripping rate can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of transmission line lightning shielding failure risk assessment, and in particular relates to a transmission line lightning shielding failure risk assessment method based on three-dimensional laser point cloud. Background Art

[0002] Practical operation and maintenance experience shows that lightning strikes are one of the main causes of tripping of overhead transmission lines. Lightning strikes mainly include two forms: shielding strike and counter-strike. For transmission lines with voltage levels of 220kV and above, due to the large dry arc distance of insulators and the high level of counter-strike lightning resistance, the probability of line tripping due to counter-strike is small, and shielding strike has in fact become the main risk source of lightning tripping accidents. Statistics of the operation of a 500kV line show that more than 90% of lightning tripping is caused by shielding strike. Conducting lightning shielding strike risk assessment for overhead transmission lines will help to discover weak points in line lightning protection and guide differentiated lightning protection transformation, which is of great significance to further improve the level of lightning protection technology for power grids.

[0003] The Electro Geometric Model (EGM) takes into account factors such as the terrain of the area where the line is located, the relative position of the ground wire, and the probability distribution of the lightning current amplitude. It can realize the quantitative calculation of the shielding risk and is widely used in the shielding risk assessment of transmission lines of various voltage levels. The basic principle of the EGM model is to draw the lightning attraction arcs of different objects according to the ground parameters and the position of the ground wire hanging point, and to evaluate whether the lightning will hit the conductor by judging the geometric relationships such as the intersection, tangency, and inclusion of the arcs. At present, key parameters such as the ground inclination angle and the coordinates of the ground wire hanging point mainly rely on manual reference to the line design drawings or on-site measurements, which is labor-intensive and the data accuracy is not high. With the introduction of ground elevation (DEM) data, it is possible to use micro-topography parameters for refined assessment of shielding risk. Some scholars have proposed to slice the single span into sections, calculate the shielding risk at each slice according to the terrain parameters extracted from the DEM data slices, and finally obtain the shielding trip rate of the entire span by weighted average. However, the actual changeable line topography makes the ground inclination change very complex along the line, and the accuracy of DEM data is limited, so the terrain parameters extracted from the two-dimensional DEM slices are poorly representative. In addition, the position of the ground wire hanging point in the span cannot usually be obtained directly from the drawings, and needs to be estimated or measured on site based on the sag. The lack of accuracy of terrain parameters and ground wire hanging point parameters limits the engineering practical effect of refined evaluation. 3D laser scanning technology was born in the 1990s. Through high-speed laser scanning measurement methods, the 3D coordinate data of the surface of the measured object can be quickly obtained with high resolution over a large area. At present, airborne 3D laser scanning technology has been widely used in 220kV and above lines, and a large number of 3D point cloud data of line channels have been obtained, laying a data foundation for carrying out refined lightning protection assessment based on 3D laser point clouds. Some scholars imitated the processing method of digital elevation models to slice the 3D laser point cloud, which can realize the high-precision extraction of parameters such as the ground wire hanging point position and ground inclination in the slice, and then realize the risk assessment of shielding failure with smaller granularity. However, this type of “slice-extract parameter” method has high computational complexity and is difficult to handle more complex situations such as multiple loops on the same tower, dense channels, and cross-spans. Therefore, its application scope is limited to simpler working conditions such as single-gear and single-loop.

[0004] The core of the traditional line shielding risk assessment method based on digital elevation model or three-dimensional laser point cloud is to perform two-dimensional slicing on the three-dimensional scene, extract the ground wire and terrain parameters from the two-dimensional slices using various graphics processing algorithms, and use the two-dimensional EGM model to calculate the lightning shielding arc. On the one hand, the method of using two-dimensional slices to extract terrain parameters is difficult to handle complex terrain, especially the situation where the terrain such as valleys, mountain tops, and slopes changes dramatically with the line direction. On the other hand, with the increasing number of multi-circuit and dense channels on the same tower, the number of ground wire hanging points in the two-dimensional slice has increased significantly. It will become very complicated to use the traditional two-dimensional EGM model to draw the shielding arc and judge the geometric relationship of the shielding arc, and it is impossible to consider the influence of cross-over, adjacent lines, etc. on the lightning shielding characteristics of the line to be evaluated. Therefore, the application scope of the traditional lightning shielding risk assessment method is still limited to simpler working conditions such as single gear and single circuit. Summary of the invention

[0005] The purpose of the present invention is to solve the deficiencies of the above-mentioned prior art, thereby providing a transmission line lightning shielding failure risk assessment method based on three-dimensional laser point cloud, which does not require complex two-dimensional slicing, parameter extraction and shielding arc geometric relationship judgment, and can realize the rapid calculation of the three-dimensional exposed arc surface area of ​​the transmission line and the accurate assessment of the line shielding failure tripping rate.

[0006] A method for assessing the risk of lightning shielding failure of a power transmission line based on a three-dimensional laser point cloud comprises the following steps:

[0007] Step 1: reclassify the three-dimensional laser point cloud data of the transmission channel, and preprocess the three-dimensional laser point cloud data and the three-dimensional laser point coordinate system;

[0008] Step 2: obtaining lightning activity parameters of the transmission channel, the lightning activity parameters including lightning density, lightning current probability distribution function and lightning incident angle probability distribution function;

[0009] Step 3: Calculate the strike distances of the conductor, ground wire, and ground point according to the given lightning current amplitude;

[0010] Step 4, using the reclassified and preprocessed three-dimensional laser point data and the calculated striking distance to draw the three-dimensional shielding arc surface of the conductor, ground wire, and ground point in the preprocessed three-dimensional laser point coordinate system;

[0011] Step 5: According to different lightning incident angles, orthogonally project the drawn three-dimensional shielding arc surface to obtain a two-dimensional exposed arc surface, and calculate the area of ​​the two-dimensional exposed arc surface;

[0012] Step 6, looping steps 3-5, calculating the exposed arc surface area under different lightning current amplitudes and lightning incident angles, and calculating the line tripping rate by combining the lightning density, lightning incident angle distribution function and lightning current probability distribution function.

[0013] Step 1 specifically includes:

[0014] Step 1.1, reclassify and color the point cloud;

[0015] Step 1.2, preprocessing the reclassified and colored point cloud;

[0016] Step 1.2.1: Point cloud thinning

[0017] The original point cloud is thinned so that the geometric distance between the thinned point clouds is no greater than a given value d, which is much smaller than the hit distance;

[0018] Step 1.2.2: Outlier removal

[0019] A statistical outlier removal (SOR) filter is used to remove outliers in point cloud samples.

[0020] Step 1.3: Adjust the coordinate system of the thinned point cloud

[0021] Draw a line connecting the center points of the large and small side towers, obtain the angle γ between the line and the y-axis of the original coordinate system, and rotate the original point cloud around the z-axis by an angle of γ, that is, multiply the original point cloud coordinates by the coordinate transformation matrix Tz(γ):

[0022]

[0023] In step 1.1, the three-dimensional laser point cloud data of the transmission channel is reclassified as follows:

[0024] The laser point cloud of the power transmission channel is reclassified into three types of point clouds related to lightning protection calculation: conductor, ground wire, and ground, and the three types of point clouds are colored;

[0025] The wire point cloud includes the original wire point cloud;

[0026] The ground line point cloud includes the original ground line, crossing line, other lines and co-wire point clouds;

[0027] The remaining original point clouds are classified as ground point clouds.

[0028] In step 1.2.2, outliers in the point cloud samples are removed, including:

[0029] Traverse all the domain points of each point in the point cloud, calculate the distance dij from each point to the domain point, where i = 1, 2, ..., m, j = 1, 2, ..., k, m is the total number of point clouds, k is the number of domain point clouds, k can be taken as 6 to 10, and calculate the neighborhood distance statistical parameters of the point cloud set:

[0030]

[0031]

[0032] Among them, μ is the average value of the neighborhood distance of the point cloud set, and σ is the standard deviation of the neighborhood distance of the point cloud set;

[0033] For point i, if its distance to the domain point satisfies the following formula, the point is judged as an outlier and removed;

[0034]

[0035] Step 2 specifically includes:

[0036] Step 2.1, query the lightning location system data, and filter out the total number of lightning strikes and the lightning current amplitude of each lightning strike in the transmission line corridor within one year;

[0037] Step 2.2: Calculate the lightning density Ng, in km-2, based on the area of ​​the transmission corridor and the total number of lightning strikes;

[0038] Step 2.3, use the log-normal distribution to count the lightning current amplitudes of the selected lightning strikes:

[0039]

[0040]

[0041] Where, f(I) is the lightning current probability distribution function, lnI is the natural logarithm of the lightning current amplitude I, a is the mean of the natural logarithm of the lightning current amplitude, and β is the standard deviation of the natural logarithm of the lightning current amplitude;

[0042] Step 2.4, define the probability distribution function of lightning incident angle distribution:

[0043] g(φ)=0.75×cos 3 (φ), -π / 2<φ<π / 2

[0044] Among them, φ is the angle between the lightning leader and the vertical direction.

[0045] In step 3, the strike distance rc of the conductor point cloud and the strike distance rgw of the ground wire point cloud are:

[0046] r c =r gw =0.67×h 0.6 I 0.74

[0047] Where h is the height of the conductor or ground line point cloud (i.e. the Z coordinate of the point cloud), and I is the lightning current amplitude;

[0048] In step 3, the hit distance rg of the ground point cloud is:

[0049] r g =0.9×I 0.65 .

[0050] Step 4 is as follows:

[0051] For any point cloud point pi(xi,yi,zi), its three-dimensional shielding arc surface is a sphere, and the spherical equation is:

[0052] (xx i ) 2 +(yy i ) 2 +(zz i ) 2 =r 2

[0053] Where r is the distance corresponding to the point cloud of this type; by taking the union of the spheres drawn by point clouds of different categories, we can get the three-dimensional shielding arc surfaces of objects of different categories.

[0054] Step 5 specifically includes:

[0055] Step 5.1, rotate the drawn three-dimensional shielding arc surface counterclockwise along the y-axis by an angle of φ, that is, multiply each point on the three-dimensional shielding arc surface by the following coordinate transformation matrix Ty(φ):

[0056]

[0057] Step 5.2, perform orthogonal projection along the Z-axis direction on the three-dimensional shielding arc surface rotated counterclockwise along the y-axis by an angle of φ to obtain a two-dimensional shielding arc surface. The scale factor in the orthogonal projection is M, that is, the actual area corresponding to each pixel of the projected two-dimensional image, and the unit is km2 / pixel;

[0058] Step 5.3, calculate the area of ​​the two-dimensional shielding arc surface at different angles:

[0059] Count the number of exposed arc surfaces of the conductor and multiply it by the projection scale factor M to obtain the area of ​​the exposed arc surface of the conductor under different lightning incident angles, in km2:

[0060] S c (I,φ)=count(p.color=red)×M.

[0061] Step 6 specifically includes:

[0062] The two-dimensional exposed arc surface area under different lightning incident angles and lightning current amplitudes is calculated cyclically, and the line shielding trip rate R is calculated based on the lightning incident angle distribution function and the lightning current amplitude distribution function. SFFOR :

[0063]

[0064] Ic and Imax are the minimum and maximum lightning current amplitudes that can cause line tripping under a given lightning incident angle φ, in kA, respectively. Among them, Imax is the minimum lightning current amplitude that makes Sc(I,φ)=0.

[0065] In view of the shortcomings of traditional shielding failure risk assessment methods, the present invention proposes a transmission line shielding failure risk assessment method based on three-dimensional laser point cloud, abandons the traditional "slicing-parameter extraction" method, and transforms the complex shielding arc geometric relationship judgment under different lightning incident angles into three-dimensional orthogonal projections at different angles by fusing the EGM model with the three-dimensional laser point cloud, thereby realizing fast and accurate transmission line shielding failure risk assessment.

[0066] Determine the strike distance of different types of objects according to the magnitude of lightning current amplitude, and use the three-dimensional laser point cloud coordinates and strike distance parameters to draw the three-dimensional shielding arc surface of the conductor, ground wire, and ground in three-dimensional space; according to different lightning incident angles, perform orthogonal projection on the three-dimensional shielding arc surface of various objects in the transmission channel to obtain the two-dimensional exposed arc surface, and calculate the area of ​​the two-dimensional exposed arc surface; cyclically calculate the two-dimensional exposed arc surface area under different lightning incident angles and lightning current amplitudes, and calculate the line shielding tripping rate by combining the lightning density, the lightning lead incident angle distribution function and the lightning current amplitude distribution function.

[0067] Compared with the traditional line shielding failure risk assessment method based on digital elevation DEM or laser point cloud, the present invention does not require complex two-dimensional slicing, parameter extraction and shielding arc geometric relationship judgment, and can realize the rapid calculation of the three-dimensional exposed arc surface area of ​​the transmission line and the accurate assessment of the line shielding failure tripping rate.

[0068] The present invention is applicable to various line installation methods, and can fully consider the influence of complex terrain, cross-overs, and adjacent lines in dense channels on lightning shielding characteristics. Compared with traditional methods, it has the significant advantages of wide application range, high evaluation accuracy, fine granularity, and simple and fast calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 To reclassify the classified laser point cloud;

[0070] Figure 2 (a) is the ground line point cloud after thinning and outlier removal; Figure 2 (b) is the ground point cloud after thinning and outlier removal; Figure 2 (c) is the wire point cloud after thinning and outlier removal; Figure 2 (d) is the synthetic point cloud of ground wire, ground surface and wire after thinning and outlier removal;

[0071] Figure 3 (a) is the original point cloud coordinate system; Figure 3(b) is the point cloud coordinate system after coordinate transformation;

[0072] Figure 4 It is a three-dimensional shielding arc surface for the conductor, ground wire, and ground point cloud;

[0073] Figure 5 (a) is a two-dimensional shielding arc surface at an angle of φ = -90°; Figure 5 (b) is a two-dimensional shielding arc surface at an angle of φ = -45°; Figure 5 (c) is a two-dimensional shielding arc surface at an angle of φ = -30°; Figure 5 (d) is the two-dimensional shielding arc surface at an angle of φ = 0°; Figure 5 (e) is a two-dimensional shielding arc surface at an angle of φ = 90°; Figure 5 (f) is a two-dimensional shielding arc surface at an angle of φ = 45°; Figure 5 (g) is a two-dimensional shielding arc surface at an angle of φ = 30°;

[0074] Figure 6 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0075] See also Figure 6 The method for assessing the risk of lightning shielding failure of power transmission lines based on three-dimensional laser point cloud of the present invention comprises the following steps:

[0076] Step 1: reclassify the three-dimensional laser point cloud data of the transmission channel, and preprocess the three-dimensional laser point cloud data and the three-dimensional laser point coordinate system;

[0077] Step 2: obtaining lightning activity parameters of the transmission channel, the lightning activity parameters including lightning density, lightning current probability distribution function and lightning incident angle probability distribution function;

[0078] Step 3: Calculate the strike distances of the conductor, ground wire, and ground point according to the given lightning current amplitude;

[0079] Step 4, using the reclassified and preprocessed three-dimensional laser point data and the calculated striking distance to draw the three-dimensional shielding arc surface of the conductor, ground wire, and ground point in the preprocessed three-dimensional laser point coordinate system;

[0080] Step 5: According to different lightning incident angles, orthogonally project the drawn three-dimensional shielding arc surface to obtain a two-dimensional exposed arc surface, and calculate the area of ​​the two-dimensional exposed arc surface;

[0081] Step 6, looping steps 3-5, calculating the exposed arc surface area under different lightning current amplitudes and lightning incident angles, and calculating the line tripping rate by combining the lightning density, lightning incident angle distribution function and lightning current probability distribution function.

[0082] Step 1 specifically includes:

[0083] Step 1.1: Reclassify and colorize the point cloud

[0084] According to the relevant standards of the State Grid Corporation, the laser point cloud of the transmission channel is usually divided into more than 20 categories, including towers, conductors, ground, vegetation, buildings, and crossovers. Among them, there are three categories related to lightning protection calculations: conductors, ground wires, and ground. The original laser point cloud is reclassified and colored according to the following rules:

[0085] Table 1 Laser point cloud classification color comparison table

[0086]

[0087] The laser point cloud after reclassification and coloring is as follows Figure 1 The point cloud coloring scheme can also be changed arbitrarily, it can be color or black and white, just modify the corresponding pixel color when counting the area in step 5;

[0088] Step 1.2: Preprocess the point cloud

[0089] The original laser point cloud has too high a point density and contains a large number of noise points and outliers, which affects the speed and accuracy of subsequent 3D shielding arc drawing. Therefore, it is necessary to first perform thinning and outlier removal on the original laser point cloud.

[0090] Step 1.2.1: Point cloud thinning

[0091] Call the equidistant thinning function in Open3D, Cloudcompare or PCL library to thin the original point cloud so that the geometric distance between the thinned point clouds is no greater than the given value d. The point cloud spacing d should be much smaller than the strike distance. For 220kV line shielding failure calculation, d can be 1 to 3m. In addition, various thinning methods such as voxel thinning and random thinning can also be used, as long as the point cloud density can be reduced and the basic structure of the ground wire is intact;

[0092] Step 1.2.2: Outlier removal

[0093] Use the statistical filter (Statistical Outlier Removal, SOR) to remove outliers in the point cloud samples. Specifically, it includes: traversing all the domain points of each point in the point cloud, calculating the distance dij from each point to the domain point, where i = 1, 2, ..., m, j = 1, 2, ..., k, m is the total number of point clouds, k is the number of domain point clouds, which can be taken as 6 to 10. Calculate the neighborhood distance statistical parameters of the point cloud set:

[0094]

[0095]

[0096] Among them, μ is the average value of the neighborhood distance of the point cloud set, and σ is the standard deviation of the neighborhood distance of the point cloud set;

[0097] For point i, if its distance to the domain point satisfies the following formula, the point is judged as an outlier and removed;

[0098]

[0099] After thinning and outlier removal, the point cloud is as follows Figure 2 As shown, Figure 2 (a) is the ground line point cloud after thinning and outlier removal; Figure 2 (b) is the ground point cloud after thinning and outlier removal; Figure 2 (c) is the wire point cloud after thinning and outlier removal; Figure 2 (d) is the synthetic point cloud of ground wire, ground and wire after thinning and outlier removal. In addition to statistical filters to remove outliers, other filters such as straight-through filtering, voxel filtering, Gaussian filtering, radius filtering, etc. can also be used as long as they can remove obvious outliers.

[0100] Step 1.3: Adjust the point cloud coordinate system

[0101] To facilitate subsequent operations such as point cloud rotation and projection transformation, the coordinate system of the original 3D point cloud needs to be adjusted. Draw a line connecting the center points of the large and small side towers to obtain the angle γ between the line and the y-axis of the original coordinate system. The original point cloud coordinate system is as follows: Figure 3 (a) As shown. The original point cloud is rotated around the z-axis by an angle of γ, and the point cloud coordinate system after the coordinate transformation is as follows Figure 3 As shown in (b), the original point cloud coordinates are multiplied by the coordinate transformation matrix Tz(γ):

[0102]

[0103] The specific implementation of step 2 includes:

[0104] Step 2.1, query the lightning location system data, and filter out the total number of lightning strikes and the lightning current amplitude of each lightning strike in the transmission line corridor within one year;

[0105] Step 2.2: Calculate the lightning density Ng, in km-2, based on the area of ​​the transmission corridor and the total number of lightning strikes.

[0106] Step 2.3, count the lightning current amplitudes of the screened lightning strikes, and use the log-normal distribution to fit the lightning current amplitude I distribution:

[0107]

[0108]

[0109] Where, lnI is the natural logarithm of I of the lightning current, mean(lnI) is the mean of the natural logarithm of the lightning current, and β is the standard deviation of the natural logarithm of the lightning current.

[0110] Step 2.4: Since the lightning leader is not vertical when it approaches the ground, the incident angle of the lightning leader needs to be considered. Use the probability distribution function of the lightning leader incident angle distribution proposed by Brown and Whitehead:

[0111] g(φ)=0.75×cos 3 (φ), -π / 2<φ<π / 2

[0112] Among them, φ is the angle between the lightning leader and the vertical direction.

[0113] The specific implementation of step 3 includes:

[0114] Step 3.1, use Eriksson's improved electrical geometry model to calculate the strike distance rc of the conductor point cloud and the strike distance rgw of the ground point cloud under the condition of a given lightning current amplitude I:

[0115] r c =r gw =0.67×h 0.6 I 0.74

[0116] Among them, h is the height of the conductor or ground wire point cloud (that is, the Z coordinate of the point cloud), and I is the lightning current amplitude.

[0117] Step 3.2, use the following formula to calculate the hit distance rg of the ground point cloud:

[0118] r g =0.9×I 0.65 .

[0119] Step 4: Draw the three-dimensional shielding arc surface of the conductor, ground wire, and ground according to the current lightning current amplitude, such as Figure 4 For any point cloud point pi(xi,yi,zi), its three-dimensional shielding arc surface is a sphere, and the spherical equation is:

[0120] (xx i ) 2 +(yy i ) 2 +(zz i ) 2 =r 2

[0121] Where r is the distance corresponding to the point cloud of this type. The spheres drawn by different types of point clouds are taken as unions to obtain the three-dimensional shielding arc surfaces of different types of objects.

[0122] Step 5 specifically includes:

[0123] Step 5.1, rotate the drawn arc surface counterclockwise along the y-axis by an angle of φ, that is, multiply each point on the arc surface by the following coordinate transformation matrix Ty(φ):

[0124]

[0125] Step 5.2: Orthogonally project the three-dimensional shielding arc surface along the Z axis to obtain a two-dimensional shielding arc surface, such as Figure 5 As shown, Figure 5 (a) is a two-dimensional shielding arc surface at an angle of φ = -90°; Figure 5 (b) is a two-dimensional shielding arc surface at an angle of φ = -45°; Figure 5 (c) is a two-dimensional shielding arc surface at an angle of φ = -30°; Figure 5 (d) is the two-dimensional shielding arc surface at an angle of φ = 0°; Figure 5 (e) is a two-dimensional shielding arc surface at an angle of φ = 90°; Figure 5 (f) is a two-dimensional shielding arc surface at an angle of φ = 45°; Figure 5 (g) is a two-dimensional shielding arc surface at an angle of φ = 30°. The scale factor in the orthogonal projection is M, which is the actual area corresponding to each pixel of the projected two-dimensional image, and the unit is km2 / pixel.

[0126] Step 5.3: Calculate the area of ​​the shielding arc at different angles.

[0127] By counting the number of red pixels (corresponding to the exposed arc surface of the conductor) in the image and multiplying it by the projection scale factor, the area of ​​the exposed arc surface of the conductor under different lightning lead incident angles can be obtained in km2:

[0128] S c (I,φ)=count(p.color=red)×M.

[0129] Step 6 specifically includes

[0130] The two-dimensional exposed arc area under different lightning incident angles and lightning current amplitudes is considered cyclically, and the tripping rate R of the conductor corresponding to different strike distance circles is calculated based on the lightning lead incident angle distribution function and the lightning current amplitude distribution function. SFFOR .

[0131]

[0132] Ic and Imax are the minimum and maximum lightning current amplitudes that can cause line tripping under a given lightning lead angle φ, respectively, in kA. Among them, Ic can be calculated from the insulator impulse breakdown test data, and Imax is the minimum lightning current amplitude that makes Sc(I,φ)=0.

Claims

1. A method for assessing the risk of lightning shielding failure of power transmission lines based on three-dimensional laser point cloud, characterized in that: The following steps are involved: Step 1: reclassify the 3D laser point cloud data of the transmission channel into three types of point clouds related to lightning protection calculation: conductor, ground wire, and ground, add colors to the three types of point clouds, and preprocess the 3D laser point cloud data and the 3D laser point coordinate system; Step 2: obtaining lightning activity parameters of the transmission channel, the lightning activity parameters including lightning density, lightning current probability distribution function and lightning incident angle probability distribution function; Step 3: Calculate the strike distances of the conductor, ground wire, and ground point according to the given lightning current amplitude; Step 4, using the reclassified and preprocessed three-dimensional laser point data and the calculated striking distance to draw the three-dimensional shielding arc surface of the conductor, ground wire, and ground point in the preprocessed three-dimensional laser point coordinate system; Step 5: According to different lightning incident angles, orthogonally project the drawn three-dimensional shielding arc surface to obtain a two-dimensional exposed arc surface, and calculate the area of ​​the two-dimensional exposed arc surface; Step 6, looping steps 3-5, calculating the exposed arc surface area under different lightning current amplitudes and lightning incident angles, and calculating the line trip rate by combining the lightning density, lightning incident angle distribution function and lightning current probability distribution function; Step 5 specifically includes: Step 5.1: Rotate the drawn three-dimensional shielding arc surface counterclockwise along the y-axis by an angle of φ, that is, multiply each point on the three-dimensional shielding arc surface by the following coordinate transformation matrix T y (φ): Step 5.2: Orthogonally project the three-dimensional shielding arc surface rotated counterclockwise along the y axis by an angle of φ along the Z axis to obtain a two-dimensional shielding arc surface. Define the scale factor in the orthogonal projection as M, which is the actual area corresponding to each pixel of the projected two-dimensional image in km. 2 / pixel; Step 5.3, calculate the area of ​​the two-dimensional shielding arc surface at different angles: Count the number of exposed arc surfaces of the conductor and multiply it by the projection scale factor M to obtain the area of ​​the exposed arc surface of the conductor at different lightning incident angles, in km. 2 : S c (I,φ)=count(p.color=conductor point cloud color)×M; Step 6 specifically includes: The two-dimensional exposed arc surface area under different lightning incident angles and lightning current amplitudes is calculated cyclically, and the line shielding trip rate R is calculated based on the lightning incident angle distribution function and the lightning current amplitude distribution function. SFFOR : Ic and Imax are the minimum and maximum lightning current amplitudes that can cause line tripping under a given lightning incident angle φ, respectively, in kA, where Imax is the minimum lightning current amplitude that makes Sc(I,φ)=0.

2. According to the method for assessing the risk of lightning shielding failure of power transmission lines based on three-dimensional laser point cloud according to claim 1, it is characterized in that: Step 1 specifically includes: Step 1.1, reclassify and color the point cloud; Step 1.2, preprocessing the reclassified and colored point cloud; Step 1.2.1: Point cloud thinning The original point cloud is thinned so that the geometric distance between the thinned point clouds is no greater than a given value d, which is much smaller than the hit distance; Step 1.2.2: Outlier removal Use statistical outlier removal (SOR) filter to remove outliers in point cloud samples; Step 1.3: Adjust the coordinate system of the thinned point cloud Draw a line connecting the center points of the large and small side towers, obtain the angle γ between the line and the y-axis of the original coordinate system, and rotate the original point cloud around the z-axis by an angle of γ, that is, multiply the original point cloud coordinates by the coordinate transformation matrix Tz(γ):

3. The method for assessing the risk of lightning shielding failure of power transmission lines based on three-dimensional laser point cloud according to claim 2 is characterized in that: In step 1.1, the three-dimensional laser point cloud data of the transmission channel is reclassified as follows: The laser point cloud of the power transmission channel is reclassified into three types of point clouds related to lightning protection calculation: conductor, ground wire, and ground, and the three types of point clouds are colored; The wire point cloud includes the original wire point cloud; The ground line point cloud includes the original ground line, crossing line, other lines and co-wire point clouds; The remaining original point clouds are classified as ground point clouds.

4. The method for assessing the risk of lightning shielding failure of power transmission lines based on three-dimensional laser point cloud according to claim 2, characterized in that: In step 1.2.2, outliers in the point cloud samples are removed, including: Traverse all the domain points of each point in the point cloud, calculate the distance dij from each point to the domain point, where i = 1, 2, ..., m, j = 1, 2, ..., k, m is the total number of point clouds, k is the number of domain point clouds, k can be taken as 6 to 10, and calculate the neighborhood distance statistical parameters of the point cloud set: Among them, μ is the average value of the neighborhood distance of the point cloud set, and σ is the standard deviation of the neighborhood distance of the point cloud set; For point i, if its distance to the domain point satisfies the following formula, the point is judged as an outlier and removed; 5. A method for assessing the risk of lightning shielding failure of power transmission lines based on three-dimensional laser point cloud according to any one of claims 1 to 4, characterized in that: Step 2 specifically includes: Step 2.1, query the lightning location system data, and filter out the total number of lightning strikes and the lightning current amplitude of each lightning strike in the transmission line corridor within one year; Step 2.2: Calculate the lightning density Ng based on the area of ​​the transmission corridor and the total number of lightning strikes, in km 2 ; Step 2.3, use the log-normal distribution to count the lightning current amplitudes of the selected lightning strikes: Where, f(I) is the lightning current probability distribution function, lnI is the natural logarithm of the lightning current amplitude I, a is the mean of the natural logarithm of the lightning current amplitude, and β is the standard deviation of the natural logarithm of the lightning current amplitude; Step 2.4, define the probability distribution function of lightning incident angle distribution: g(φ)=0.75×cos 3 (φ), -π / 2<φ<π / 2 Among them, φ is the angle between the lightning leader and the vertical direction.

6. The method for assessing the risk of lightning shielding failure of power transmission lines based on three-dimensional laser point cloud according to claim 5, characterized in that: In step 3, the strike distance rc of the conductor point cloud and the strike distance rgw of the ground wire point cloud are: r c =r gw =0.67×h 0.6 I 0.74 Where h is the height of the conductor or ground line point cloud (i.e. the Z coordinate of the point cloud), and I is the lightning current amplitude; In step 3, the hit distance rg of the ground point cloud is: r g ＝0.9×I 0.65 。 7. A method for assessing the risk of lightning shielding failure of power transmission lines based on three-dimensional laser point cloud according to claim 1, 2, 3, 4 or 6, characterized in that: Step 4 is as follows: For any point cloud point pi(xi,yi,zi), its three-dimensional shielding arc surface is a sphere, and the spherical equation is: (x-x i ) 2 +(y-y i ) 2 +(z-z i ) 2 =r 2 Where r is the distance corresponding to the point cloud of this type; by taking the union of the spheres drawn by point clouds of different categories, we can get the three-dimensional shielding arc surfaces of objects of different categories.

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